I had a similar problem with one of my frames. What your missing is a detent ball, there's two, one on each side of the hammer. What I would recommend is contacting James Henry, he's in CA. He will either fix the hammer or replace it with a new one, that's what I opted for. If you send it back to the factory they will do the 'easy open' conversion, that I did not want done.
Send me a PM and I'll give you his contact info. or do a search here. I'm sure it's on one of the boards.